针对较大基数的排列组合算法Java实现类（n选m）

package com.utils;

import java.math.BigDecimal;
import java.math.RoundingMode;

public class PLZUUtils {

public static BigDecimal computePaiLie(int n, int m) {
if(m > n || n < 0 || m < 0) {
throw new IllegalArgumentException("n必须大于m!");
}
return computerJC(n).divide(computerJC(n - m), 1, RoundingMode.HALF_UP);
}

public static BigDecimal computeZuhe(int n, int m) {
if(m > n || n < 0 || m < 0) {
throw new IllegalArgumentException("n必须大于m!");
}
//=n!/m!(n-m)!

return computerJC(n).divide((computerJC(m).multiply(computerJC(n - m)).setScale(1, RoundingMode.HALF_UP)), 1, RoundingMode.HALF_UP);
}

public static BigDecimal computerJC(int n) {
if(n < 0) {
throw new IllegalArgumentException("n不能为负数!");
} else if(n == 0) {
return new BigDecimal(1);
}
BigDecimal bd = new BigDecimal(1.0);
for(int i=n; i>=1; i--) {
bd = bd.multiply(new BigDecimal(i)).setScale(1, RoundingMode.HALF_UP);
}
return bd;
}

public static void main(String[] args) {
BigDecimal zh = computeZuhe(462, 442);
System.out.println(zh.doubleValue());
}

}